Buggy code:
public abstract class Page extends MarkupContainer implements IRedirectListener , IRequestablePage { private static final int FLAG_IS_DIRTY = FLAG_RESERVED3 ; private static final int FLAG_PREVENT_DIRTY = FLAG_RESERVED4 ; private static final int FLAG_STATELESS_HINT = FLAG_RESERVED5 ; private static final int FLAG_WAS_CREATED_BOOKMARKABLE = FLAG_RESERVED8 ; private static final Logger log = LoggerFactory . getLogger ( Page . class ) ; private static final ConcurrentHashMap < String , Boolean > pageClassToBookmarkableCache = new ConcurrentHashMap < String , Boolean > ( ) ; private static final long serialVersionUID = 1L ; private int autoIndex ; private int numericId ; private transient Set < Component > renderedComponents ; private transient Boolean stateless = null ; private final PageParameters pageParameters ; private int renderCount = 0 ; protected Page ( ) { } protected Page ( final IModel < ? > model ) { } protected Page ( final PageParameters parameters ) { } private Page ( final PageParameters parameters , IModel < ? > model ) { } public PageParameters getPageParameters ( ) { } public final void componentRendered ( final Component component ) { } @ Override public void detachModels ( ) { } @ Override public void internalPrepareForRender ( boolean setRenderingFlag ) { <START_BUG> if ( ! ( getFlag ( FLAG_INITIALIZED ) ) ) { <END_BUG> internalInitialize ( ) ; } super . internalPrepareForRender ( setRenderingFlag ) ; } public final void dirty ( ) { } public boolean setFreezePageId ( boolean freeze ) { } public final void dirty ( final boolean isInitialization ) { } public final void endComponentRender ( Component component ) { } public final int getAutoIndex ( ) { } @ Override public final String getId ( ) { } public final Class < ? extends Page > getPageClass ( ) { } @ Override public final long getSizeInBytes ( ) { } @ Override public final boolean getStatelessHint ( ) { } public final String hierarchyAsString ( ) { } public boolean isBookmarkable ( ) { } public boolean isErrorPage ( ) { } private boolean peekPageStateless ( ) { } public final boolean isPageStateless ( ) { } public final void onRedirect ( ) { } public final void setNumericId ( final int id ) { } public final void setStatelessHint ( boolean value ) { } public final void startComponentRender ( Component component ) { } @ Override public String toString ( ) { } private void checkRendering ( final MarkupContainer renderedContainer ) { } private void init ( ) { } private void setNextAvailableId ( ) { } protected void componentChanged ( Component component , MarkupContainer parent ) { } protected void configureResponse ( ) { } @ Override protected final void internalOnModelChanged ( ) { } @ Override protected void onBeforeRender ( ) { } @ Override protected void onAfterRender ( ) { } @ Override protected void onDetach ( ) { } @ Override protected void onRender ( ) { } final void componentAdded ( final Component component ) { } final void componentModelChanging ( final Component component ) { } final void componentRemoved ( final Component component ) { } final void componentStateChanging ( final Component component ) { } void setPageStateless ( Boolean stateless ) { } @ Override public MarkupType getMarkupType ( ) { } public PageReference getPageReference ( ) { } public int getPageId ( ) { } public int getRenderCount ( ) { } public final void setWasCreatedBookmarkable ( boolean wasCreatedBookmarkable ) { } public final boolean wasCreatedBookmarkable ( ) { } public void renderPage ( ) { } public final boolean wasRendered ( Component component ) { } }

Fix:
if ( ! ( isInitialized ( ) ) ) {